ENDOCRINE SYSTEM TOPICS

Transcription

1 ENDOCRINE SYSTEM TOPICS PART ONE: BASIC HORMONES 3:30 PART TWO: HYPOTHALAMUS & PITUITARY GLAND PART THREE: THYROID & PARATHYROID GLANDS 7:24 PART FOUR: ADRENAL GLAND & PANCREAS 10:04 PART FIVE: PINEAL GLAND & OTHER TISSUES 2:45 1

2 ENDOCRINE SYSTEM The endocrine system is made of various glands spread throughout the body. There are three glands in the brain, the hypothalamus, pituitary gland, and the pineal gland. The thyroid gland is in the neck. In the abdomen we can find the pancreas behind the stomach. On top of each kidney are the adrenal glands. In men the testes are part of the endocrine system, while in women, the ovaries are part of the endocrine system. There are a number of other hormone producing glands that are not a part of the endocrine system. Some of these hormone producing areas are the stomach, intestines, thymus, heart, fat, etc. These other tissues or organs will be discussed in greater detail in their own respective chapters. Hypothalamus Pineal Gland Pituitary Gland Thyroid Gland Adrenal Glands Pancreas Ovaries (females) Testes (males) 2

3 HORMONE ACTION The endocrine system uses glands to release chemicals called hormones into the blood. These hormones travel throughout the entire body and will target any cell that has receptors for that hormone. Because hormones have effects on tissues all over the body, the action of that hormone depends on the membrane receptor and the target cell. Like testosterone increasing hair production from facial hair follicles or sperm production in the testes. Same hormone, different action depending on where the cell is and what that cell does. The nervous system and endocrine system are both communication systems within our body but they differ in a number of ways. The nervous system uses nerves instead of hormones. The nervous system is a hardwired system like a land line telephone, it only communicates with what it is directly connected to. This allows the nervous system to be much faster than the endocrine system. The endocrine system takes minutes to hours to work while the nervous system is virtually instantaneous. Water Soluble Hormones Hormones are classified as either water soluble or lipid soluble. Water soluble hormones are proteinbased and have receptors, like a docking station, that is on the surface of a cell membrane. These receptors have to be on the outside of a cell because water soluble hormones cannot cross the lipid bilayer that makes up the cell membrane. Once the hormone binds with the outer receptor, it starts a chemical cascade called a second messenger system which then causes something to happen inside the cell, usually release pre made proteins. Lipid Soluble Hormones Lipid soluble hormones are cholesterol based and can go right through the cell membrane to connect to receptors or docking stations inside the cell. Once the hormone binds to the receptor inside the cell, it can activate activity within the nucleus. Lipid soluble hormones must access DNA strands to create the new proteins, this takes longer than water soluble s release of ready made proteins and the formation of new proteins have many implications in health and disease, specifically cancer. 3

4 HYPOTHALAMUS The hypothalamus is located in the diencephalon, below the thalamus. The hypothalamus is one of the primary autonomic control centers of our body. This is how we maintain control over many of the function of our body that we don t have to think about, like blood pressure, testosterone or estrogen production, sperm or egg Hypothalamus development, thirst control, hunger cravings, metabolism, etc. In order to maintain homeostasis over so many Pituitary gland Infundibulum different types of physiological processes, the hypothalamus receives many different types of information (blood pressure, hormone levels, electrolyte balance, etc). Once a particular parameter is considered to be out of homeostasis or out of balance, the hypothalamus then communicates with the pituitary gland to fix the problem or carry out an action. What is important to understand is that the hypothalamus does not directly control any organ or tissue, it only controls the pituitary gland. The pituitary gland will then target the tissues or organs of the body. The hypothalamus is connected to the pituitary gland, by a thin connection called the infundibulum. The pituitary gland is located inferior to the hypothalamus and is encased within the sella turcica of the sphenoid bone. The pituitary gland is divided into two parts: anterior and posterior. The anterior pituitary is controlled by hormones released by the hypothalamus. The hormones from the hypothalamus to the anterior pituitary gland, travel through a two capillary bed network called the hypophyseal portal system, located within the infundibulum. There are two groups of hormones made by the hypothalamus to control the anterior pituitary gland. Releasing" hormones travel to the anterior pituitary gland to initiate the release a particular hormone out to the body. "Inhibiting hormones travel to the anterior pituitary gland to stop the release of a particular hormone. The posterior pituitary is controlled by nerves coming from the hypothalamus through the infundibulum. The nerves that control the posterior pituitary gland have cell bodies in the hypothalamus and axon terminals in the posterior pituitary gland. The action from the hypothalamus to the posterior pituitary gland involves direct nerve control. This causes chemicals from the neuron to be released in the posterior pituitary gland, then sent out to the body. Summary: Hypothalamus Located in the diencephalon Receives information from the body about autonomic functions Controls the pituitary gland to cause an effect on the body Pituitary control through two pathways: releasing or inhibiting hormones through the hypophyseal portal system and direct nerve control 4

5 PITUITARY GLAND The pituitary gland is located inferior to the hypothalamus, encased within the sella turcica of the sphenoid bone. It is connected to the hypothalamus by a stalk called the infundibulum. The pituitary gland is also called the hypophysis which means to grow beneath. The pituitary gland has two distinct regions, anterior and posterior, both of which secrete hormones to the body. The posterior pituitary gland is also known as the neurohypophysis where neuro refers to the fact that it is made entirely of nerves and controlled by nerve impulses from the hypothalamus. This exemplifies the direct neural connection between the posterior pituitary and the hypothalamus. On a histology slide, the posterior pituitary gland has a more uniform or plain appearance in comparison to the anterior pituitary gland. There are two hormones released out to the body from this region of the pituitary gland: antidiuretic hormone and oxytocin. Posterior Pituitary Antidiuretic hormone targets the kidney tubules to retain water under conditions of dehydration or high solute or electrolyte concentration. The result of reduced water excretion is balanced electrolyte levels and increased blood volume. It acts as a don t pee hormone. Oxytocin is a powerful hormone that targets smooth muscle, specifically the uterus and milk ducts in the breast. It stimulates uterine contraction during labor, stimulates milk ejection or let down of milk, and plays a role in orgasm in both men and women. Other actions of oxytocin are not well defined. 5

6 Anterior Pituitary The anterior pituitary gland is also known as the adenohypophysis where adeno means gland. It is controlled by hormones travelling from the hypothalamus through the hypophyseal portal system in the infundibulum. The anterior pituitary gland contains many different cells to produce about 6 different hormones. On a histology slide, you can see a number of color variations indicating the many different cell types. Thyroid stimulating hormone is released by the anterior pituitary and targets only the thyroid gland. The action on the thyroid gland is to release the thyroid hormones, T3 and T4, which increase metabolism, under normal conditions. The stimulus sequence begins with the hypothalamus detecting low metabolism. The hypothalamus then sends out thyrotropin releasing hormone to the anterior pituitary, which then sends out thyroid stimulating hormone. Thyroid stimulating hormone then circulates throughout the body to finally act on its target, the thyroid gland. Adrenocorticotropic hormone does what its name is. Adreno indicates it is going to the adrenal gland, cortico indicates it is going to the cortex or outer region of the adrenal gland and tropic indicates that its target is specific to that area, nowhere else in the body. Once adrenocorticotropic hormone targets the adrenal cortex, it will release a family of hormones called glucocorticoids. Cortisol is the main stress hormone in this family that is released. This process begins when the hypothalamus detects a state of stress. The hypothalamus then sends out corticotropin releasing hormone through the hypophyseal portal system to the anterior pituitary. The anterior pituitary then sends out adrenocorticotropic hormone throughout the body targeting the adrenal cortex, which in turn releases cortisol (actions discussed in adrenal gland section). Luteinizing hormone is released by the anterior pituitary gland targeting the gonads stimulating the release of sex steroids. In women, luteinizing hormone targets the ovary to release of estrogen and a luteinizing hormone surge in mid cycle will cause an egg to be released. In men, luteinizing hormone targets the testes to increase testosterone production. The hypothalamus detects circulating testosterone and estrogen levels. When these levels are low, the hypothalamus sends gonadotropin releasing hormone through the hypophyseal portal system to the anterior pituitary gland. Luteinizing hormone is then released, targeting the gonads to increase sex steroid production. There are also a number of other hormones and reproductive factors that affect the hypothalamus control of this hormone that are beyond the scope of our course. Follicle stimulating hormone is released by the anterior pituitary gland targeting the gonads to stimulate gamete production. In women, follicle stimulating hormone targets the ovary to develop an egg for ovulation. In men, follicle stimulating hormone targets the testes to increase and support sperm production. The hypothalamus regulates the gamete production cycle, which vary considerably from male to female and will be discussed in greater detail in the reproductive system chapter. Prolactin is released by the anterior pituitary gland with receptors all over the body. Prolactin binding to receptors located on mammary glands (breast tissue) cause milk production in lactating women. Both men and women have prolactin, although the role of prolactin in men is not clearly defined. Although 6

7 there are prolactin receptors all over the body, the role of this complex hormone outside of milk production is poorly understood. Growth hormone is released by the anterior pituitary gland and targets tissues all over the body. Its primary purpose is for skeleton growth in children at the epiphyseal plates as well as musculature. It increases protein synthesis (as occurs with muscle or tissue building), increases lipid breakdown and mobilization of fatty acids, and affects on insulin and blood glucose levels. When the hypothalamus initiates the release of growth hormone from the anterior pituitary gland, it sends out growth hormone releasing hormone into the hypophyseal portal system. The pituitary gland then releases growth hormone. Deep sleep in children is associated with a surge of growth hormone release. Summary: Pituitary Gland Located under the hypothalamus in the brain Histological features: two distinct regions (anterior and posterior) Anterior pituitary gland releases 6 hormone to know Posterior pituitary gland releases 2 hormones 7

8 THYROID GLAND The thyroid gland is located on the anterior side of the neck. You can feel it under the skin, just below the Adams apple and between the sternocleidomastoid muscles. Lift your chin upward slightly to palpate the gland. The thyroid gland is shaped like a bow tie, with a narrow central region called the isthmus. On either side of the isthmus, the thyroid gland enlarges into a right lobe and a left lobe. When we look at a thin slice of the thyroid gland under a microscope under low power, we first notice a pattern of many circles. Looking more closely we can see dots surrounding the pink colored circles. Then at high power, it becomes more clear that the dots surrounding the circles are actually cells. You may see some red blood cells in the areas around the large pink circles, this is common as all glands have a lot of blood vessels within them to allow the hormones from those gland to readily enter the circulation. The large pink circular areas are called follicles. These follicles are filled with a large molecule called thyroglobulin which is a storage form for the thyroid hormones T3 and T4. Surrounding each follicle, are follicular cells. These are made of simple cuboidal epithelial tissue and are the target for thyroid stimulating hormone from the anterior pituitary gland. Thyroid stimulating hormone from the anterior pituitary gland targets these follicular cells to initiate the release of the thyroid hormones, T3 and T4 from within the follicles into the blood stream and out to the cells of the body. The cells in the areas outside of and adjacent to the follicles are called parafollicular cells. Parafollicular cells are also known as C cells because they produce the calcium hormone Calcitonin. Calcitonin is the third hormone produced by the thyroid gland. It is produced by the parafollicular cells located outside of the pink follicles. Calcitonin targets the bones of the skeletal system and the kidneys for calcium regulation. The role of calcitonin is to lower blood calcium levels. Calcitonin accomplishes this in two ways. Calcitonin targets the kidney tubules to excrete more calcium out into the urine and by targeting the bones to take up more calcium for storage. High blood calcium levels, not the pituitary gland, initiate the release of calcitonin from the thyroid gland. The main hormone produced by the thyroid gland is tetraiodothyronine most commonly called T4 or Thyroxine. The thyroid also produces triiodothyronine, commonly called T3. T3 is produced by the thyroid in much smaller quantities; however T3 is the more bioactive form that is preferred by the cells of the body. These hormones are made by the follicular cells and stored in the many large follicular pools found within the thyroid gland. 8

9 T3 and T4 from the follicular cells of the thyroid gland have an effect on all the cells of our body. Its primary function is related to lipid and carbohydrate metabolism and the basal metabolic rate. In children, T3 and T4 play a role in growth and brain development. The stimulus to release these thyroid hormones comes from thyroid stimulating hormone from the anterior pituitary gland. When the basal metabolic rate of the body has slowed down, it is detected by the hypothalamus, which sends thyrotropin releasing hormone to the anterior pituitary gland, then the anterior pituitary releases thyroid stimulating hormone to the thyroid gland, which in turn releases T3 and T4. T4 and T3 are each named for how many iodines they have attached. Tetraiodothyronine has four iodine molecules and triiodothyronine has three iodine molecules. T3 is the bioactive form that is most readily utilized by our bodies cells to increase mitochondrial metabolism. Since the thyroid gland makes mostly T4, and very little T3, each cell must take in the T4 and use an enzyme to cut off an iodine to make their own T3. Under normal conditions, the iodine that the enzyme removes makes T3 that increases metabolism. Recently it has been found that under stressful conditions, a different iodine molecule is removed which makes reverse T3 causing a decrease in metabolism. This is an important finding because this explains what is going on in patients that have hypothyroid symptoms but have lab work indicating normal amounts of T3 and T4. Only recently have laboratories been able to test specifically for normal T3 and for reverse T3. Summary: Thyroid Gland Located in the neck with a narrow central region and enlarges as it wraps around the airway Histological features: circular pools called follicles, surrounded by follicular cells, with adjacent parafollicular cells Releases two hormones that affect metabolism (T3 and T4) and calcitonin which decreases blood calcium levels Pituitary control through two pathways: releasing or inhibiting hormones through the hypophyseal portal system and direct nerve control PARATHYROID GLAND There are four separate small glands located on the posterior surface of the thyroid gland called parathyroid glands. The main hormone produced by these glands is parathyroid hormone, produced by chief cells. Its role is to increase blood calcium levels. It is the most important regulator of calcium and phosphorus in the body. Parathyroid hormone targets the bones, kidneys, and intestines to increase blood calcium. Kidneys are stimulated to retain calcium, calcium is taken out of bones, and more calcium is absorbed from food by the intestines. All of this works together to increase blood calcium levels for use in a variety of chemical and physiological processes. Therefore, the stimulus to release parathyroid hormone is low blood calcium levels. 9

10 ADRENAL GLAND The adrenal gland is located inside the retroperitoneal cavity and sits on top of each kidney. The adrenal gland is two glands in one. The adrenal cortex is the outer region or crust. The adrenal medulla is the middle region. Think of the adrenal gland like a jelly donut, with the inner jelly part the medulla. Like the donut part of a jelly donut, the cortex portion goes all the way around. Adrenal Cortex The adrenal cortex has three distinct layers called zona. Starting from the outermost layer, there is the zona glomerulosa, zona fasciculata, and zona reticularis. The zona glomerulosa releases a family of hormones called mineralcorticoids. The main hormone from this family is aldosterone. Aldosterone acts on the kidney tubules to retain sodium and water which increases blood volume and can increase blood pressure. Aldosterone also increases potassium excretion via the urine. Mineralcorticoid release is stimulated by high extracellular potassium levels and a powerful blood pressure hormone called aldosterone II. The zona fasciculata releases a family of hormones called glucocorticoids. The most common is hydrocortisone, Adrenal Cortex better known as cortisol. All cells in the body have receptors for these hormones. The main effect is to increase fat use, conserve glucose by increasing formation but reducing use so blood glucose levels remain elevated. Adrenal Medulla In addition, cortisol can increase abdominal fat accumulation which has recently been shown to dramatically increase cardiovascular disease risk in a combination of factors called Metabolic Syndrome. There are known anti inflammatory effects, which is why a form of this hormone is used clinically as an anti inflammatory. Adrenocorticotropic hormone from the anterior pituitary gland is the main stimulus to release glucocortiocids. The process begins with the hypthalamus within the brain sensing stress (physiological like damage or psychological) and releases corticotropin releasing hormone through the hypophyseal portal system to the anterior pituitary. The anterior pituitary then sends out adrenocorticotropic hormone throughout the body targeting the zona fasciculata of the adrenal cortex. The zona reticularis secretes sex hormones, primarily androgens like testosterone. However, estrogen can also be made from this region. Testosterone increases male like secondary sex characteristics like increased muscle mass, and facial hair growth. This zona is stimulated to release hormones by circulating sex hormone levels. 10

11 Adrenal Medulla The adrenal medulla secretes the hormones of the sympathetic nervous system, epinephrine and norepinephrine. They target alpha and beta receptors, which have a multitude of functions all over the body. Their collective effects follow the flight or fight rule such as increased heart rate, pupil dilation, etc. Anything that will activate your autonomic nervous system sympathetic response like being scared will increase the release of these hormones. The release of these hormones allow our heightened physiological response to danger be sustained over a longer period of time. The example is when you get frightened you instantly feel the tightening of your stomach, this is the instantaneous nervous system effect. Then when you realize the danger was something like the wind and are no longer scared but your heart is still beating strongly for many minutes afterward, that is the sustained effect of the norepineprhine and epinephrine released as hormones. They take much longer to be removed from the circulation. Summary: Adrenal Gland Located on top of the kidney, made of two different glands (adrenal cortex and adrenal medulla) Histological features: cortex region wraps around medulla. Cortex contains three zona, medulla is just a group of cells in the center. Adrenal cortex releases several groups of hormones from the three zona: mineralcorticoids from zona glomerulosa, glucocorticoids from zona fasiculata, and androgens and sex hormones from the zona reticularis. Adrenal medulla releases two hormones of the sympathetic nervous system: epinephrine and norepinephrine. 11

12 PANCREAS The pancreas is located deep inside the abdominal cavity. It is hidden under and behind the stomach. When the stomach is removed you can see the long pancreas, with a head tucked next to the first turn of the duodenum or small intestine and a tapered tail next to the spleen. This location near the intestine allows it to easily secrete the digestive enzymes for food processing. Islet of Langerhans Acini When a slice of the pancreas is removed and stained it looks fairly uniform with variations of purple. Acini are the clusters exocrine glands that are stained purple. Pancreatic acini secrete digestive enzymes that go through the pancreatic duct into the small intestine or duodenum. These exocrine cells make up the majority of the pancreatic tissue.the few light pink or pale regions are called Islets of Langerhans; some areas are large and some are small. These Islets are the endocrine portion of the pancreas which contain alpha and beta cells that produce the hormones glucagon and insulin, respectively. These hormones affect blood glucose levels. Insulin is required by our cells to shuttle glucose inside. All cells use glucose to make ATP for energy, in order to get the glucose in, insulin is required. When blood glucose levels are high, like after a meal, insulin is released from the Islets of Langerhans into the blood to help move the absorbed glucose from the blood into cells. When the working cells have enough glucose to meet their immediate energy needs, insulin helps to store excess glucose. Short term storage regions like the liver, store the glucose as glycogen while fat is where we store glucose for long term storage. Between meals when blood glucose levels drop and we are hungry, glucagon is released by the pancreas. Glucagon allows glucose that has been stored to be released into the blood, thus increasing blood glucose levels. The increased glucose levels allow our cells to maintain energy until we eat again. Summary: Pancreas Located in the abdominal cavity under the stomach Histological features: dark pink acini exocrine glands secrete digestive enzymes, lighter regions called Islet of Langerhans endocrine cells release insulin and glucagon Releases two hormones: insulin lowers blood glucose by increasing cell uptake, glucagon raises blood glucose by releasing glucagon from storage areas. 12

13 Negative Feedback Loop for Insulin Negative Feedback Loop for Glucagon Eat carbohydrate Hungry (between meals) Absorbed as glucose Blood sugar level drops, below normal Blood sugar levels increase, above normal levels Islet of Langerhan s α cells release glucagon Islet of Langerhan s β cells release insulin Insulin attaches to receptors on cells to help each to cell take in glucose from the blood Glucagon stimulates liver to breakdown glycogen into glucose to be released into the blood Blood sugar levels increase, back to normal levels Insulin helps liver cells take extra glucose and store it as glycogen for use later, between meals α cells stop releasing glucagon Blood sugar level drops, to normal β cells stop releasing insulin Type I Diabetes Mellitus Type I Diabetes Mellitus is an auto immune disease where the person's own immune system attacks the beta cells in the Islets of Langerhans. This reduces the amount of insulin that the pancreas can release. When blood glucose levels rise after a meal, the glucose cannot enter cells to be used for energy. These patients must inject insulin after every meal to facilitate glucose uptake into cells. If they don t, blood glucose levels become very high while the cells are starving for glucose since it can't enter the cell without insulin. This condition has traditionally been called "Juvenile onset diabetes" as most patients are diagnosed when they are young. Type II Diabetes Mellitus Type II Diabetes Mellitus is due to the desensitization of insulin receptors due to chronically high blood glucose levels and over insulin production. This develops over several years of excessive glucose and therefore excessive insulin levels. Patients are required to decrease 'simple' carbohydrate intake (carbohydrates that break down quickly like sugar). In extreme cases patients must inject insulin because extra insulin is needed for cells to operate the glucose shuttle system. The goal of any treatment is to reduce the glucose levels and insulin that the cells are exposed to in order to re sensitize the receptors so that they can operate properly. Exercise and diet are the best long term solutions for this problem. Exercise is even more effective at insulin receptor resensitization than any drug on the market. 13

14 PINEAL GLAND The pineal gland is located in the posterior region of the diencephalon as part of the epithalamus. The pineal gland is a light sensitive gland that secretes the hormone melatonin. When the gland senses decreasing light levels or darkness, it increases the release of melatonin. Melatonin affects the circadian rhythm or 24 hour body clock regulating our sleep wake cycles. As cortisol levels decline in the evening when we become sleepy, melatonin levels increase. This relationship may explain why it is difficult for people to fall asleep when they are stressed and have high cortisol levels. In animals, melatonin plays a role in seasonal behavior such as mating or hibernation based on the seasonal changes in daylight exposure. Melatonin has antioxidant properties which can reduce free radicals in the brain as well as aid the immune system. Increased melatonin levels are associated with increased growth hormone secretion in children. Summary: Pineal Gland Located in the posterior region of the diencephalon (can be seen between posterior cerebrum and cerebellum). Pineal gland releases melatonin which regulates the sleep wake cycle. Melatonin has been found to have effects on a number of other systems and functions, however these mechanisms are not yet clearly understood. 14

15 OTHER ENDOCRINE TISSUES When studying the endocrine system, it is important to know that hormone producing tissues are not limited to those glands that are classified as a part of the endocrine system. There are many other tissues or organs that release hormones while also performing other primary functions. A few of these tissues are described briefly. The intestines have a primary function of digesting food and absorbing nutrients. In these processes, hormones are released to control the rate of food entering the intestines by the stomach, hormones to control the release of bile from the gall bladder, hormones to control the release of digestive enzymes from the pancreas, and other control needs. The specific hormones will be discusses in the gastrointestinal chapter. The kidneys have a primary function of filtering our blood, but also releases three different hormones. The hormones of the kidney affect blood pressure, oxygen delivery by increasing red blood cell production, and calcium absorption from the gut. The heart is our main organ for propelling blood throughout our circulatory system. It also can release a hormone which will lower blood pressure. The thymus is an important organ of the immune system with hormones that regulate the development of cells that aid our immunity to foreign invaders. Adipose is fat storage but even fat can release hormones. Leptin is a hormone that affects the hypothalamus and plays a role with appetite. 15

16 ENDOCRINE SUMMARY PART ONE: BASIC HORMONES 1. Describe the similarities and differences between the nervous and the endocrine systems. The nervous and endocrine systems both are means of cells communicating with other cells to cause an effect. The nervous system utilizes nerves which release neurotransmitters onto receptors on the surface of a specific cell. The time course of neuroactivation is very fast, within milliseconds. The endocrine system utilizes glands which release hormones into the blood to circulate throughout the entire systemic circulation. The target for the hormones are on the surface of cells with specific receptors for that hormone. They may be in specific areas of the body or all over. 2. What is the difference between endocrine and exocrine glands? Endocrine glands secrete their product into the blood to circulate through the systemic circulation. Exocrine glands secrete their product out through ducts to a specific place (surface or in a cavity). 3. Describe how hormones are classified as either water soluble or lipid soluble and give examples of both types. Water soluble hormones are amino acid derivatives or peptide hormones. They target receptors on the surface of cells, activating a second messenger system to elicit an action or the release of pre made proteins. o Example: insulin, melatonin, calcitonin, growth hormone Lipid soluble hormones must travel through the blood on a carrier protein. They are steroid hormones or eicosanoids. Lipid soluble hormones target receptors inside the cell, as they can easily cross the lipid bilayer of cell membranes. They cause activation within the nucleus to produce the production of new proteins. o Example: estrogen, progesterone, testosterone, cortisol, aldosterone 4. Describe how water soluble hormones interact with a cell to cause a specific outcome. Water soluble hormones target receptors on the surface of cells, activating a secondmessenger system to elicit an action or the release of pre made proteins. 5. Describe how lipid soluble hormones interact with a cell to cause a specific outcome. Lipid soluble hormones target receptors inside the cell, as they can easily cross the lipid bilayer of cell membranes. They cause activation within the nucleus to produce the production of new proteins. 16

17 PART TWO: HYPOTHALAMUS & PITUITARY 1. Describe the location of the hypothalamus and its relationship to the pituitary gland. The hypothalamus is located within the diencephalon below the thalamus. The pituitary gland is located within the sella turcica. The hypothalamus and pituitary gland is connected to via a stalk called the infundibulum. 2. Describe the function of the hypothalamus. The hypothalamus monitors a myriad of functions throughout the body (thirst, electrolyte balance, hunger, cold, stress, reproductive cycle, sleep, etc.). To control or alter systemic physiological function, the hypothalamus communicates with the pituitary gland to send pituitary hormones targeting specific tissues. 3. Describe how the hypothalamus controls the adenohypophysis. The hypothalamus sends inhibiting or releasing hormones through the hypophyseal portal system to the adenohypophysis, anterior pituitary gland, to stimulate or inhibit specific pituitary hormone release. 4. Describe how the hypothalamus controls the neurohypophysis. The hypothalamus communicates directly with the neurohypophysis, posterior pituitary gland, via nerves and neurotransmitters to stimulate the release of antidiuretic hormone or oxytocin. 5. What are the hormones produced by the hypothalamus and what are their targets? The hypothalamus produces a number of releasing hormones and a number of inhibiting hormones that travel through the hypophyseal portal system to the adenohypophysis. 6. What are the hormones produced by the anterior pituitary gland? For each hormone, indicate its target and action. Thyroid stimulating hormone: Targets the follicular cells of the thyroid to stimulate the formation of tetraiodothyronine (T4 or thyroxine) and triiodothyronine (T3). Adrenocorticotropic hormone: Targets the zona fasciculata of the adrenal cortex to cause the release of glucocorticoids. Follicle stimulating hormone: Targets follicles in the ovary and Spermatogonia in the Seminiferous tubules in the testes. Stimulates gamete production (egg and sperm, respectively). Luteinizing hormone: Targets thecal cells in the ovary and Leidig cells in the testes to produce hormones (estrogen and testosterone, respectively). In females, a mid cycle surge stimulates ovum release from the ovary. Prolactin: Receptors are located all over the body with many unknown functions. The known function is to stimulate milk production in mammary glands. Growth hormone: targets all cells in the body, particularly the liver where it is converted into insulin growth factor 1. It stimulates growth and increased metabolism. Melanocyte stimulating hormone: you don t need to know this one. 17

18 7. What are the hormones produced by the posterior pituitary gland? For each hormone, indicate its target and action. Antidiuretic hormone: target is the distal convoluted tubules of the kidneys to cause the reabsorption of sodium and water. Oxytocin: many targets throughout the body. Uterus and milk ducts are some. Oxytocin stimulates uterine contractions during labor or orgasm, and milk ejection during lactation. 8. Describe the conditions associated with excessive growth hormone. Acromegaly is due to an excessive production of growth hormone during adulthood. Result is greater than normal growth in the soft tissues and flat bones. 9. Describe the condition associated with insufficient growth hormone. Pituitary dwarfism is due to an insufficient production of growth hormone during childhood growth. Result is less than normal growth. 10. Describe the condition associated with insufficient antidiuretic hormone. Diabetes insipidus is due to the lack of antidiuretic hormone from the neurohypophysis. This alters water conservation mechanisms in the body allowing the release of excessive amounts of water. PART THREE: THYROID & PARATHYROID 1. Describe the location of the thyroid and parathyroid glands. The thyroid gland is located in the neck, wrapping around the trachea. The four glands are found on the posterior surface of the trachea, two on each side. 2. Name the hormones produced by the thyroid gland. For each hormone: (1) name the action of that hormone, (2) name the cell that produces that hormone, and (3) indicate what activates the release of that hormone. Tetraiodothyronine (T4 or thyroxine) o Targets mitochondria of all cells, it becomes activated when enzymes cleave off an iodine. It increases mitochondrial action (metabolism). o Produced by follicular cells. o The release is activated by the presence of thyroid stimulating hormone from the adenohypophysis. Triiodothyronine (T3) o Targets mitochondria of all cells. It can increase or decrease mitochondrial action (metabolism), depending on what iodine has been cleaved off. o Produced by follicular cells. o The release is activated by the presence of thyroid stimulating hormone from the adenohypophysis. Calcitonin 18

19 o Targets bones and kidneys. In the bone it inhibits osteoclast activity and during youth it stimulates osteoblast activity. In the kidneys it increases calcium excretion. o Produced by parafollicular cells (C cells). o The release is activated by elevated calcium levels in the blood. 3. Name the hormones produced by the parathyroid thyroid glands. For each hormone: (1) name the action of that hormone, (2) name the cell that produces that hormone, and (3) indicate what activates the release of that hormone. Parathyroid hormone o Targets bone, kidneys, and indirectly the GI tract. In the bone, it stimulates osteoclasts to increase calcium release and inhibits ostoblasts. In the kidneys, it increases the reabsorption of calcium. Also in the kidneys it stimulates another hormone, Calcitriol that increases calcium and phosphate absorption from the GI tract. o Produced by chief cells. o The release is activated by a reduction in blood calcium levels. 4. Describe the difference between normal T3 and reverse T3, including structure and action. Normal T3 activates the mitochondria to increase metabolism. It is formed by an iodine being removed from T4. Reverse T2 inhibits mitochondrial action, decreasing metabolism. It is formed by the removal of a different iodine component from T4 than for normal T3. This difference in structure causes a much different effect at the cellular level. 5. Describe the activation and inactivation process (negative feedback loop) for tetraiodothyronine. o Hypothalamus detects low metabolism o Hypothalamus releases thryotropin releasing hormone, targeting the anterior pituitary gland. o The anterior pituitary gland releases thyroid stimulating hormone targeting the follicular cells of the thyroid gland. o Thyroid gland releases T3 and T4. o T3 and T4 target cells all over the body to increase the mitochondrial activity and metabolism. o Hypothalamus detects normal metabolism activity o Hypothalamus releases thyrotropin inhibiting hormone to stop the release of thyroid stimulating hormone and subsequent activation of the thyroid gland. 6. Describe the activation and inactivation process (negative feedback loop) for calcitonin. o Parafollicular cells detect high blood calcium levels. o Parafollicular cells release calcitonin. o Calcitonin targets bone to uptake calcium and kidneys to excrete calcium. o Parafollicular cells detect normal blood calcium levels. o Parafollicular cells stop the release of calcitonin. 19

20 PART FOUR: ADRENAL GLAND & PANCREAS 1. Describe the location of the adrenal cortex and the zona. The adrenal cortex surrounds the medulla. It is made of three layers called zona. Each zona secretes a particular group of hormones. 2. Describe the location of the adrenal medulla. The adrenal medulla is the inner core of the adrenal gland. It is made of modified nervous tissue so it releases norepinephrine and epinephrine into the blood. 3. Describe the location of the pancreas and the endocrine regions of the pancreas. The pancreas is located inferior to the stomach. The pancreas is primarily made of acini that release digestive enzymes into the small intestine (duodenum). There are small regions called the Islets of Langerhans that release the hormones glucagon and insulin that are released in response to low or high levels of blood glucose, respectively. 4. List the 3 zona of the adrenal cortex. For each zona: (1) name the group of type of hormone that is produced, (2) name a specific hormone, and (3) indicate the action of that hormone. Zona glomerulosa o Mineral corticoids o Aldosterone o Increased sodium retention and water retention by the kidneys Zona fasciculata o Glucocorticoids o Corticosterone, cortisol o Anti inflammatory effects, altered glucose utilization Zona reticularis o Androgens and sex hormones o Estrogen, testosterone o Activate secondary sex characteristics (body hair growth,, etc.) 5. Name the hormones produced by the adrenal medulla and describe what those hormones do. Norepinephrine and epinephrine mimic the effects of the sympathetic nervous system allowing stimulation over a longer time course than via the nervous system alone. 6. Describe a negative feedback loop for activation and inactivation of the zona glomerulosa. Low blood pressure Increased release of aldosterone Increased sodium reabsorption and water reabsorption by kidneys so blood volume is increased Blood pressure returns to normal Inhibition of aldosterone release 7. What is the exocrine function of the pancreas? The pancreatic acini makes enzymes that digest carbohydrates, fats, and proteins. These enzymes are secreted in to the duodenum of the small intestine. 8. Name the endocrine region of the pancreas and the hormones produced by that region. 20

21 The islet of Langerhan s produce glucagon and insulin. o Glucagon comes from alpha cells that increase the breakdown of glycogen stores, increasing blood glucose levels (between meals). o Insulin comes from beta cells that increase the cellular uptake of glucose, decreasing blood glucose levels. This is important immediately after a meal has been consumed. 9. Describe Type I diabetes. Type I diabetes occurs when the immune system targets beta cells for destruction causing the impairment of insulin production. People with type I diabetes must inject an appropriate amount of insulin after every meal to help the cells take in glucose for energy. 10. Describe Type II diabetes. Type II diabetes occurs after many years of excessive insulin production due to excessive and chronic high blood glucose levels. The high insulin production over many years causes the insulin receptors on the cells to become desensitized to insulin so the beta cells must produce more insulin than it normally needed to in order to get the cells to take in the glucose. o Treatment is to decrease the high glucose levels in the body and resensitize the insulin receptors so the body does not have to make so much insulin to get the job done. Exercise is the best receptor resensitizing treatment you can do because it tells the cells that glucose is needed for energy. Drugs available that also resensitize insulin receptors but none can do it to the level that basic exercise can. o In serious cases, insulin injections may be needed because the insulin receptors are so desensitized that the body can t produce enough insulin to get the glucose into the cells so additional insulin is needed to keep the person alive. Ideally that person needs to get their insulin receptors resensitized as soon as possible because doing insulin injections is not curing the problem at all, it is actually perpetuating the problem. PART FIVE: PINEAL GLAND & OTHER TISSUES 1. Describe the location of the pineal gland. The epithalamus in the diencephalon, above the thalamus. The largest portion is found on the posterior surface of the diencephalon above the corpora quadrigemina. 2. Describe the hormone produced by the pineal gland and what that hormone does. Melatonin release is activated by the absence of light. It facilitates sleep wake patterns and plays a primary role in seasonal behaviors and hormone production seen in animals (hibernation, mating, increased hair growth for winter before the temperature drops, etc.). In humans it plays a major role in coordinating many hormone release patterns. 21

22 3. Provide a list of other organs that have endocrine functions (but have other primary functions) and a hormone that they produce. Intestines: digestive regulatory hormones Kidneys: renin for blood pressure, erythropoietin for red blood cell production, and calcitriol for calcium absorption. Heart: atrial natriuretic peptide for blood pressure reduction Thymus: immune system hormones for the specific defenses Adipose tissue: leptin for hunger and satiety 22

23 ENDOCRINE STUDY ACTIVITIES EXERCISE 1: HORMONES For each hormone listed, please indicate the gland and specific region or cells the hormone comes from, and the action of that hormone. HORMONE GLAND REGION OR CELLS ACTION 1 Oxytocin Pituitary Posterior Smooth muscle contractions 2 Antidiuretic Hormone 3 Thyroid stimulating hormone 4 Adrenocorticotropic hormone 5 Luteinizing hormone 6 Follicle stimulating hormone 7 Prolactin Men: Women: Men: Women: 8 Growth hormone 9 T3/T4 10 Calcitonin 11 Parathyroid hormone 12 Aldosterone 13 Cortisol 14 Androgens & sex hormones 15 Epinephrine & Norepinephrine 16 Insulin 17 Glucagon 18 Melatonin 23

24 EXERCISE 2: HISTOLOGY For each histology image, indicate the gland that image comes from and the cells or regions indicated. Gland. List the hormones produced by region B. List the hormones produced by region A. A. B. Gland. List the hormones produced by cells indicated in B. A. cells (circled in red) List the hormone produced by cells indicated by the red circles. B. cells Gland. List the hormones produced by region B. List the 3 classes of hormones produced by region A. A. B. Gland. A. List the hormones produced by cells indicated in A. What is produced by region B? A B. 24

25 EXERCISE 3: BRAIN GLANDS Please label and color the regions indicated. Pineal Gland Hypothalamus Adenohypophysis Neurohyophysis Hypophyseal Portal System 25

26 EXERCISE 4: THYROID & PARATHYROID ANATOMY Please label and color the regions indicated. anterior posterior Thyroid Gland Parathyroid Glands (4) Follicular Cells (Thyroid Gland) Hormone produced: Para follicular Cells (Thyroid Gland) Hormone produced: Histology image from thyroid gland 26

27 EXERCISE 5: PANCREAS ANATOMY Please label and color the regions indicated. Pancreas Islet of Langerhans Hormone produced: Hormone produced: Acini Products produced: 27

28 Exercise 6: Adrenal Gland Anatomy Please label and color the regions indicated. Zona Glomerulosa Hormone family or group produced: Name one of those hormones: Zona Fasciculata Hormone family or group produced: Name one of those hormones: Zona Reticularis Hormone family or group produced: Name one of those hormones: Adrenal Medulla Hormones produced (2): 28

29 ENDOCRINE STUDY QUESTIONS THESE QUESTIONS ARE INTENDED TO GUIDE YOU TOWARD A DETAIL AND EMPHASIS IN STUDYING BY TRYING TO HELP CONNECT SEVERAL CONCEPTS TOGETHER. IT IS IMPORTANT TO FIND THE RIGHT ANSWER(S), AS WELL AS KNOW WHY THE WRONG ANSWERS ARE INCORRECT. 1. One benefit that water soluble hormones have over lipid soluble hormones is that. a. they have an ability to transverse the cell membrane b. they are slower and longer acting c. they activate pre made proteins, thus are quicker to end result d. they act in a more local area e. All of the above 2. Which of the following statements is true? May be more than one. a. Pancreatic hormones can activate the activity in a cell s nucleus b. Steroid hormones have direct action and receptors inside the cell c. Thyroid stimulating hormone activates the release of other hormones d. Sex hormones use a camp 2 nd messenger system 3. Which gland produces inhibiting or releasing hormones that do not travel all over the body? a. Pituitary gland b. Neurohypophysis c. Hypothalamus d. Adenohypophysis e. Adrenal gland 4. Which hormones does the adenohypophysis (anterior pituitary) release? a. Antidiuretic hormone b. Thyroid stimulating hormone c. Releasing hormones d. Adrenocorticotropic hormone e. Luteinizing hormone f. Inhibiting hormones g. Prolactin h. Oxytocin i. Growth hormones j. Follicle stimulating hormones 29

30 5. Which hormones does the posterior pituitary or neurohypophysis release? a. Antidiuretic hormone b. Thyroid stimulating hormone c. Releasing hormones d. Adrenocorticotropic hormone e. Luteinizing hormone f. Inhibiting hormones g. Prolactin h. Oxytocin i. Growth hormones j. Follicle stimulating hormones 6. Which hormones does the hypothalamus create and release? a. Antidiuretic hormone b. Thyroid stimulating hormone c. Releasing hormones d. Adrenocorticotropic hormone e. Luteinizing hormone f. Inhibiting hormones g. Prolactin h. Oxytocin i. Growth hormones j. Follicle stimulating hormone 7. What hormone has the effect of releasing glucocorticoids? a. Oxytocin b. Luteinizing Hormone c. Growth hormone d. Adrenocorticotropic hormone e. Tetraiodothyronine 8. Lutenizing hormone. a. is produced in the gonads b. causes gametes to be released from an ovary c. stimulates sperm and egg maturation d. stimulates the production of testosterone e. A, B, and C are correct f. B and D are correct 30

31 9. Follicular cells. a. are cells found between follicles that produce calcitonin b. produce both T 4 and T 3 c. are simple cuboidal cells arranged in a circle in the thyroid d. are targeted by thyroid stimulating hormone from anterior pituitary e. B, C and D is correct f. All of the above are correct 10. What hormone is increased by stress and decreases metabolism? a. Tetraiodothyronine or T4 b. Reverse triiodothyronine or rt3 c. Normal triiodothyronine or T3 d. Aldosterone e. Glucagon 11. Which of the following is true? a. Triiodothyronine or T3 is also called Thyroxine b. Calcitonin is a hormone from the thyroid that lowers blood calcium levels c. Thyroid stimulating hormone has the greatest cellular effect on the mitochondria of cells in the body d. Calcitonin is increased by thyroxine 12. After the hypothalamus detects low metabolism and stimulates the adenohypophysis with thyrotropin releasing hormone the. a. posterior pituitary releases thyrotropin b. thyroid releases T 3 and T 4 to increase metabolism of cells c. thyroid is stimulated by the thyroid stimulating hormone d. posterior pituitary releases thyroid stimulating hormone (TSH) 13. Which of the following is a true statement regarding the adrenal cortex? a. Cortisol is a glucocorticoids that is produced in the zona reticularis. b. Corticosterone and cortisol are produced in the zona glomerulosa. c. Mineralcorticoids like aldosterone alter the concentration of electrolytes in the blood (which affects blood pressure). d. Testosterone is produced in the zona glomerulosa. 31